1. Field of the Invention
A parking brake arrangement includes an operating lever pivotally movable between brake-applied and brake-released positions, with locking means for releasably locking the lever in the brake-applied position, and self-adjust cable slack removing means for automatically removing cable slack when the lever is in the brake-released position, at least one of the locking and cable slack removing means including internal spring clutch means.
2. Brief Description of the Prior Art
It is well known in the vehicle parking brake art to provide self-adjust means for removing cable slack when the operating lever is in the brake-released position, as evidenced by the U.S. Pat. Nos. to Porter et al 4,841,798 and Hass et al 4,850,242, each assigned to the same assignee as the present invention. In the Hass et al patent, it is proposed to obtain "soft" release operation of the parking brake lever by the use of spring clutch means of the external clutch spring and drum type. In the Porter et al patent, as illustrated in FIGS. 1 and 2, when the parking brake mechanism is in the fully released condition, the adjuster/track sub-assembly 26, 24 is allowed to freely rotate in a direction so as to cause greater cable tension until a point of equilibrium is reached, thereby insuring a minimum tension and lack of cable slack at each stroke. The lock pawl 30 is held out by the lock pawl release lever 64 which is rotated to the "release position" by the pedal owing to the engagement between lever 12 and button 66. The drive pawl 32 is held out of engagement with ratchet teeth 18b by a fixed tab 10e on the mounting bracket 10, thereby allowing free rotation of the self-adjuster in either the clockwise or the counter clockwise direction. The ends 26a and 26b of the preloaded spring 26 react between the drive stud 27 and with the ratchet pivot sleeve 20, thereby to rotate the ratchet 18 and the cable tract 24 in the cable-tensioning direction relative to lever 12. Thus, the advantage is presented of "over adjust" safeguard, owing to the lock pawl 20 and drive pawl 32 being maintained in the disengaged condition.
When the operator applies a brake-engaging force to the pedal 12, rotation direction about the main pivot axis 14 is initiated. Owing to the drive pawl 32 being fixed between the pedal 12 and the drive plate 16, it begins to rotate away from the fixed tab 10e, thereby allowing the drive pawl 32 to engage in the ratchet teeth 18a to initiate cable take up. At this point, the ratchet 18 is connected with the pedal 12, and both legs of the adjuster spring 26a and 26b are locked so as to retain spring position during the "apply" and "lock" cycle. After a specified amount of stroke otherwise known as "free travel", the lock pawl release lever 64 is rotated to an off position by the release lever spring 60 which in turn allows the lock pawl 30 to engage in the ratchet 18, thereby allowing the cable load to be held by the connection between ratchet 18 and the mounting bracket means 10. As the operator continues the brake-applying force, at a point designed to be the end of the "free travel" , the pedal pawl 52 engages pedal ratchet notches 12e integral with the lever 12. At any time after the pedal pawl (52) begins to ratchet, the operator's foot may be removed and the mechanism will maintain the resultant cable load. At the time that the operator's foot is removed, the pedal pawl 52 is driven to the end of an internal slot 52a and at the same time the pedal 12 "back drives" to an intermediate position. The drive pawl 32 is relieved, and at this time the adjuster spring end 26a is allowed to relax, insuring that the lock pawl 30 is fully engaged in a notch of the ratchet 18, thereby holding the cable load.
After the parking brake system has been set, upon actuation of the manual release lever 58 (either manually by the manual release control means 59, or automatically by the vacuum means 72 upon the starting of the vehicle), the manual release lever 58 pivots about its pivot shaft 50 to cause the pedal pawl 52 to rotate to a released position, thereby disengaging the pedal teeth 12e to allow the pedal 12 to rotate in the clockwise direction, owing to the force created by the adjuster spring end 26a transmitted through the drive stud 27.
As evidenced by the Perisho et al U.S. Pat. No. 5,182,963 (also assigned to the same assignee as the present invention), it has been proposed to provide in the parking brake mechanism art clutch spring mechanisms including drums that are formed of porous or sintered metal impregnated with a damping oil, thereby to achieve improved long-lasting soft-release operation of the parking brake operating lever.
Other spring clutch arrangements are disclosed in the U.S. Pat. No. to Briggs No. 1,965,878, Havada No. 4,651,854, Matoukak et al No. 5,011,237 and Ojima et al No. 5,275,262.
In the prior systems, use has been made of spring clutches of the external type--i.e., the clutch spring is generally arranged concentrically about a companion drum member for frictional engagement with the external surface thereof. In the case of a self-adjust cable slack adjuster system, the clutch spring and the cable track biasing spring require a substantial amount of space, thereby increasing the size and cost of the parking brake mechanism. The present invention was developed to incorporate spring clutches of the internal type, thereby to provide space for a larger torsion spring for rotatably biasing the cable track member in the slack-removing direction. A further advantage is that the anchoring of the internal clutch spring is not as critical as in an external clutch spring, and the turns of the spring permit an allowable stress that is higher in compression than in tension. The spring clutch affords infinite position adjustment with finite travel, and the "skipout" which occurs with conventional ratchet and pawl locking mechanisms is avoided.